Method and apparatus for metallic coating of metallic strands



Nov. 24, 1959 E. L. KNAPP 2,914,423

METHOD AND APPARATUS FOR METALLIC COATING 0F METALLIC STRANDS Filed Sept. 26, 1956 S Sheets-Sheet 1 reducinggg cr 1265.2 g

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E. L. KNAPP METHOD AND APPARATUS FOR METALLIC COATING OF METALLIC STRANDS Filed Sept. 26. 1956 3 Sheets-Sheet 2 m? A a a w J m m4 3:

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E. L. KNAPP Nov. 24, 1959 METHOD AND APPARATUS FOR METALLIC COATING 0F METALLIC STRANDS Filed Sept. 26, 1956 3 Sheets-Sheet 3 INVENTOR. 5 4. MAP/z A T RN YS.

United States Patent "ice METHOD AND APPARATUS FOR METALLIC COATING OF METALLIC STRANDS Earle L. Knapp, Kansas City, Mo., assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Application September 26, 1956, Serial No. 612,274

31 Claims. (Cl. 118-102) This invention relates to continuous coating of metallic strands with molten metal. While the invention has been illustrated herein in connection with the coating of wire, it will be understood that the invention is not so limited and that it could be applied to strip. Hence, where the term strand has been used in the specification and claims it should be understood to be inclusive of wire and strip. The strand may be of iron or steel and any of the conventional coating metals may be used with minor changes, such as Zinc, zinc containing small amounts of aluminum, alloys of aluminum, tin, terne, and the like.

This application is a continuation-in-part of my copending application Serial No. 507,825, filed May 12, 1955, and now abandoned.

The Sendzimir patents, Nos. 2,110,893, 2,136,957, and 2,197,622 disclose procedures which are in commercial use in the hot coating of metal strip. In accordance with the teachings of thesepatents, a scale-free strip or wire is cleaned by the removal of oils, greases and the like, and is then subjected to a heat treatment in a reducing atmosphere and carried beneath the surface of the bath of molten coating metal while under the protection of the reducing atmosphere whereby the use of entrance flux is avoided. The metal enters the bath at a temperature close to the bath temperature and the surfaces of the metal to be coated are in condition to be rapidly and thoroughly wetted by the molten coating metal.

I By way of example, a specific procedure involves carrying an iron ir steel strip in a scale-free cold rolled condition through an oxidizing furnace wherein the oils and greases and the like are burned off the surface of the strip and a very thin controlled coating of oxide is formed thereon. According to another exemplary procedure, alkali or other chemical cleaning which involves wetting and drying of the surface of the strip may be used. The thin oxide coating formed by the cleaning pretreatment is reduced in the reducing furnace.

This procedure and other known procedures have, in the coating step, always involved the passage of a metallic strand through a bath of molten coating metal with which the strand remains in contact for appreciable length of time. This results in the contamination 'of the molten coating metal bath with the metal of the strands to be coated. Thus, in baths of molten coating metal capable of dissolving iron, considerable quantities of dross will be formed. In cases where aluminum or alloys rich in aluminum are being used as the coating metal and the wire or strand to be coated is of iron, the bath rapidly becomes saturated with iron. Large quantities of iron in the molten aluminum are undesirable since, for example, the coating will be less ductile and have a lower corrosion resistance.

Various attempts to reduce the pick-up of iron by the molten bath have been made but these have been generally unsuccessful in solving the problem. Apparently the first successful attempt involved a procedure disclosed in a copending application in. the name of Oganowski,

Serial No. 372,073, filed August 3, 1953. According to 2,914,423 Patented Nov. 24, 1959 this disclosure the strand issuing from the coating bath was contacted by a lip element above the normal level of metal in the bath and the strand drew the molten coating metal upwardly under the lip, so that the molten coating metal at the lip was under negative head. In this way, the application of a molten coating metal was confined to an area which was so short in the direction of motion of the strand that the molten coating metal applied to the strand was carried away by the strand without opportunity for reflux into the bath. In the coating of a strip, lips were provided for each side of the strip and the lips were staggered so as to cause the strip at each lip to be deflected a slight amount.

It is an object of the present invention to provide a method and an apparatus for coating a strand whereby reflux of coating metal into the bath is also minimized or avoided, but without physically contacting the strand with anything in the nature of a lip, wiper or scraper.

It is another object of the present invention to provide for the production of coated strand at high speed. In the conventional wire coating methods currently in use, some sort of a wipe is employed at the surface of the bath to control the uniformity and weight of the coating on the wire. Such a wipe tends to take off a large proportion of the free metallic coating down to the alloy layer which is stronger and .firmly attached to the base metal. When using the teachings of the Sendzimir Patent No. 2,197,622 above referred to, there is a minimum of alloy layer and therefore it becomes too easy to remove almost all of the zinc. It is, therefore, yet another object of the invention to provide for the use of fluid friction for wiping excess molten coat ing metal from the strand with no direct mechanical contact between the apparatus and the surface of a coated strand at its final dimensions, and this irrespective of the specific type of pretreatment, and irrespective of the specific type of coating procedure involved.

These and other objects of the invention which will be discussed in greater detail hereinafter, I accomplish by the construction and arrangement of parts and by that series of method steps of which I shall now disclose an exemplary embodiment.

Reference is made to the drawings forming a part hereof and in which:

Figure 1 is a fragmentary somewhat diagrammatic plan view of a coating pot for use in the coating of wire strands.

Figure 2 is a greatly enlarged fragmentary cross-sectional view taken on the line 22 of Figure 1.

Figure 3 is a fragmentary cross-sectional view taken on the line 33 of Figure 2.

Figure 4 is a fragmentary diagrammatic view showing the cross-section of an apparatus for introducing a wire into the pot.

Figure 5 is a greatly enlarged diagrammatic View showinng the bottom of the coating pot and the coating control means in relation to the wire being coated.

Figures 6 to 9 inclusive are diagrammatic representations showing effects of variations in extent of the coating control element and clearance between it and the wire being coated.

- Figure 10 is a diagram similar to Figure 5 showing an altgrnative arrangement useful under certain conditions, an

Figure 11 is a diagrammatic representation showing the effect of an arrangement according to Figure 10.

Briefly, in the practice of the invention, the strand to be coated, which in the example illustrated is a wire,

comes preferably from a pretreating apparatus according to the Sendzimir patents and is brought to the coating' upwardly through an'orifice in the bottom of a pot, 'and' the bottom of the pot about the orifice slopes upwardly to the orifice. Thus, if the strand being coated is a wire, the bottom of the pot may be in the form of a shallow cone having an orifice for thepassage of the strand at the-apex thereof. The orifice is of such size as to provide for a slight clearance about the strand and means are provided for centering the strand in relation to the orifice.

The strand continues upwardly and passes through a coating control element. This element generally will comprise a first portion which is of a material which is wettable by the molten coating metal and a succeeding portion which is of a material which is not wetted by the molten coating metal. As will be pointed out hereinafter, under certain conditions, if the coating metal is one having a tough and gummy oxide, the first portion of thecoating control element, i.e. that portion which is of wettable material, may be omitted, and likewise it may be unnecessary to operate at a negative head. The wire passes through an aperture in the control element with clearance about the wire, and it may then pass through a protective hood filled with non-oxidizing gas. It will be understood that conventional means (not shown) will be provided for moving the strand through the apparatus.

Referring more particularly to the drawings, a coating pot reservoir is indicated at having what might be termed a coating pot manifold 11 with a plurality of individual pot extensions 12. Conventional means are provided for heating the reservoir, manifold and pot extensions. Dams 11a (one such dam is shown in position in Figure 1) may be provided so that an individual pot extension 12 may be disconnected from the manifold 11, when it is desired to cut out a strand, or to rethread, or the like. The individual extensions 12 may be built in two parts, so that the portions 12a may be removed for threading or the like. In each of the extensions 12 there is an orifice 13 and the bottom of the pot at 14- slopes away in all directions so that the bottom is in elfect in the form of a shallow cone with the orifice 13 at its apex.

In Figure 4, the strand, which in this instance is a wire, is indicated at 15 and is shown as passing around a roll or pulley 16 and thence upwardly to the bath. Pairs of rollers 17, 17a and 18, 18a are provided for aligning the wire 15 with the orifice 13 in the pot. Since the wire has preferably been treated as directed in the Sendzimir patents, it will come to the pot in a reducing atmosphere within a hood 19. In situations where it is impractical to provide a gas tight connection between the hood and orifice, the reducing gases within the hood 19 will be under a slight pressure so that they will issue from the end of the hood 19, as indicated at 20, to protect the wire 15 until its-entrance into the orifice 13. It will be understood that in place of the rollers or pulleys 17, 17a, 18, 18a, a wire drawing die 18b (Figure 5) or the like may be used for aligning the wire with the orifice 13 4 alloy. This alloy is nominally considered to contain 20% chromium, 20% cobalt, 20% nickel, balance iron. A detailed analysis of the alloy is given in Metal Data by S. L. Hoyt, Reinhold Publishing Co. (1952), in Table 372, on page 349.

At the start of a run, the level of molten metal in the pot will be such that the molten metal contacts the strand as it passes upward from the orifice in the bottom of the pot extension but as soon as the coating metal has contacted the strand, the level of the metal in the pot is lowered below the edge of the orifice so that the molten coating metal is in effect pulled upwardly out of thebath by the moving strand, so that the coating metal, as it is being applied to the strand, may be said to be under negative head. In restarting a pot extension after rethreading or the like, an additional amount of molten coating metal may be placed in the extension before the dam is removed, so that before the dam is removed the level of coating metal will momentarily be high enough to wet the strand and restart the operation as above outlined.

If wire is being coated at very low speeds, say for example a few feet per minute, wire may be coated by simply withdrawing it vertically from an open pot. Where, however, wire is being coated at high speeds on the order of 300 to 500 feet per minute, the wire no longer can be withdrawn from an open pot if a smooth, uniform surface is desired. At high speeds, the wire strand tends to pull the oxide or surface scum off of the surface of a molten metal in the coating pot faster than it can form and the aperture in the coating control element described hereinafter. A pair of rolls 49-41 may be provided above the chamber 23 for moving the strand upwardly through the orifice in a continuous manner, said rolls being driven in conventional manner. Alignment of the strand with the orifice 13 is important to prevent the coating metal from running out, and also to avoid pulling an oxide skin through the aperture in the said coating control element. The die or the guiding wheels or pulleys should preferably contain no carbon inany form. If the die or the at the place the wire is exiting from the bath. When this occurs, broken areas or patches of oxide film will pull up the wire rather than a continuous film and, while a continuous uniform oxide film will support a uniform thickness of coating metal underneath the oxide film, a discontinuous oxide film will cause an accumulation of oxide and coating metal on the wire which will solidify in a nonuniform manner, referred'to by the art as berries" on the wire. In order to provide for successful highspeed operation, means must be provided to prevent heavy oxide and excess coating metal from being drawn up in a meniscus around the wire issuing from the top of the coating bath and being carried off as an accumulation on the surface of the wire.

When working with molten metals that tend to form oxide scums, precautions must be taken so that the scams or oxide films are not disturbed. When exposed to air, the molten metal oxidizes and an oxide film forms over a certain surface area. When the shape of the surface is changed, the solid film will tend to buckle or bunch up or accumulate in one area, thus causing an unevenness in the coating. The oxide has a certain weight and strength and resistance to deformation. When withdrawing a wire vertically from the surface of a bath, the oxide film might be likened to a sac in the shape of a cone. If pulled upward too much, it will eventually distend and rupture, causing a glob of oxide film to be withdrawn on the surface of the wire. If, instead, an anchoring plate can be positioned so as to anchor the oxide film near the apex of the above mentioned cone, the wire will continue to withdraw molten aluminum at a uniform rate and the coating will be smooth and concentric, especially if a neutral atmosphere or finishing gas is used in the hood 23, so that when the oxide film does reform as at 31 and the coating solidifies, equilibrium conditions will have been reached between run back, forward motion of the wire, cohesion, ctc., giving a uniform symmetrical coating of a controlled thickness.

To control the amount and distribution of coating metal on the wire, I provide what may be thought ofas a coating control element or as a combination of two elements. The first of these which I shall hereinafter refer to as an anchoring plate is indicated at 21 andis made of a material whichis wetted by the molten coating metal. The anchoring plate 21 may, for example, be of steel or castironor, for minimum-iron pick up, itimay' 5 be made of-titanium bearing cast iron or preferably of molybdenum. b

The other part of the controlelement is indicated at 22 and is made of a material which is not wetted by themolten coating metal. The member 22 is of a ceramic material such as, for example,'zirconium silicate, porcelain, fire clay, or even an oxidized steel surface coated with lime. 'The lime coated oxidized steel surface has the disadvantage oflow abrasion resistance.

gas so as to insure that the coating has become dimensionally stable before it comes into contact with the atmosphere. Thereafterv any oxide coating which is formed cannot disturbthe surface finish. The factors here involved aregdiscussed in the Coburn Patent No. 2,526,731, dated October ZA, 1950.

Coating quality (with respect to the absence of brittle interrnetallic alloys) is a function of the time the coating metal is in contact with the steel strand at high temperature. The growth of undesirable brittle intermetallic alloys proceeds while the strandis immersed in the molten metal bath, while the coating metal remains in moltencond tion on the strand before solidification, and even while the coating is at high'temperature after solidification. It is therefore important that the strand after coating be cooled rapidly, as for exampleby air jets, located above the gas finishing chamber 23 if used.

j By way of explanationofthe theory of operation of this invention, the coating metal, as it is withdrawn from the bath, will have an oxide skin formedupon it. This skin will anchor to theanchoring plate 21 which is wettable by the molten coating metal, and the nonwettable control element 22 repels the coating metal from climbing furtherwith' the, wire. If the height of the anchoring plate 21 is kept below that height to which a meniscus would climbif the strand were just withdrawn from an open bath atthe same speed, the oxide skin will anchor to the plate 21 at a position radially distant from the aperture in the plate 21 such that there will be no tendency for the oxide surface film to be pulled into the aperture, only pure unoxidized and uncontaminated coatingmetal will be pulled up from the bath underneath the oxide layer or skin and onto the strand.

The anchoring plate 21 may be said to stabilize the shape. of the meniscus and to define the extent and strengthen mechanically the oxide film on the meniscus. No preformed oxide can,.there fore, be carried onto the surface of the coated wire. In Figures 6 to 9 inclusive the preformed oxide onthe meniscus which anchors to the anchoring plate is indicated at 30. New oxide forms on the coating and on the wire as at 31 in these figures; or if non-oxidizing finishing gas is used in the hood 23, the natural oxide will form more slowly. I The molten coating metal has considerable coherence so that when a layer of it adheresto the moving wire it carries additional coating metal up to the anchoring plate, the amount so carried or pumped up being related directly to the viscosity ofthe molten coating metal, the roughness of the surface of the strand, and the speed of the strand. Since this plate is of a wettable material, the coatingmetal would be pulled up through the coatingv apparatus and would occupy a position such as is indicated by the broken'lines 30a in Figure 6. This action is prevented by the element 22awhich is of nonwettingmaterial and as a result of this the coating metal willtake a shape such as shown at 31 in Figure 6.

The situation demonstratedby the lines 30a in Figure 6 might also result if the wire speed is too high. could be overcome by changing the dimension A '.(Fig. 5) to that shown, for example, in Figure 7. Thus, it can be seen that for higher wire speeds, the non-wet table element 22 must have a greater longitudinal extent as at 22b in Figure 7. A change in thickness of the anchoring plate 21, as indicated by the dimension B will aifect the weight of the coating. The thicker the plate or the larger the dimension B, the greater the weight of coating produced since the pumping action of the wire would be enhanced. A decrease in the dimension D, as illustrated by comparing Figure 8 with Figure 7, will decrease the weight of coating because it restricts the amount of molten coating metal which is being drawn upwardly. In considering the weight of coating or the amount of coating metal carried out of the coating apparatus on the surface of the wire, it should be remembered that while the apparatus is in operation at any reasonable speed, there will be coating metal available at the top surface of the anchoring plate 21. The temperature relationship between the strand and the coating metal, and the fluidity of the coating metal will affect the length of time or the distance that it will take for the rapidly traveling strand and the effect of gravity to cause a stable position to be reached with regard to coating thickness. A relatively hot strand, with hot coating metal and at slow speed would result in a thin coating. If the dimension C (Fig. 5) is increased, a still lighter weight of coating will be produced, as shown in Figure 9.

Since the pumping action of the wire is a function of its speed, an increase in the speed of operation will build up the meniscus under the anchor plate to a larger diameter and give a heavier weight of coating. Hence, if it is desired to decrease'the weight of coating, the element 21 must be raised to a point where the meniscus is reduced in diameter, as shown by comparing Figure 9 with Figure 8.

As far as dimension E (Fig. 5) is concerned, it is obvious that it should not be so great that molten coating metal will run down through orifice 13. I have found that this dimension is not critical; the clearance can be great enough to permit the coating of a moderate range in wire size without changing the orifice. I believe that there is little tendency for the molten metal to run out because of its low positive head above the orifice. This tendency can be decreased further by constructing the bottom of the pot, or the orifice at least, of non-wetting material. I have found that aluminum is less likely-to run out than zinc. Therefore, when aluminum is used, the clearance may be somewhat larger.

7 Similarly, on account of the characteristics of the molten coating metal, the degree of the slope of the bottom 14 of the pot can be steeper when coating with aluminum than when coating with zinc. The zinc oxides are not as tough and strong as the aluminum layer and they, therefore, cannot be drawn uphill as well as the aluminum oxide. Also, the normal operating level of the molten metal will generally have to be somewhat higher for zinc than for aluminum and for the same reasons. It is to be understood that it is permissible'to use forms of slopes leading up to the orifice, other than the conical form of the example, the determining factor being the ability of the coating metal to be pulled upward over angular surfaces as would be the'case if a stepped cylinder were to be substituted for the cone shown at 14.

The size of the aperture in the control element 22 bears some relationto the final size of the coated strand, but it is not necessarily the same. The final size of the coated product is not determined by the size of the aperture only; it does not wipe the coating down to final size. By a control of the clearance between the wire and the anchoring plate and between the wire and the non-wettable control element and by the extent of these elements in the direction of movement of the wire'and the distance between initial contact of the coating metal with the wire and the'anchoring plate, as well as by control of the =inetal level in the pot, the

thickness of the coating may be controlled.

In an example of actual practice, we have coated 16 gauge wire at 300 feet per minute with the level of aluminum of an inch below the edge of the orifice.

Dimension A was /2 inch, B was inch, C was 1% inches, D was .050 inch, and E .040 inch. In an eX- emplary operation with zinc, with the same gauge of Wire and coating speed, we have used the operating level of the bath at /2 inch below the edge of the orifice.

Dimensions A, B, and D were the same as for aluminum; "C was of an inch, and dimension E was .020 inch.

While I prefer to use the wettable anchoring plate 21, it has been found possible to eliminate this wettable element and operate only with the non wetting element. This situation is illustrated in Figure 10. It will be noted that here I am no longer operating with a negative head, in that the operating level of the bath is the same as the starting level. By comparison with Figure it will be observed that the dimension C is about one-half of C in Figure 5, and that the dimension D is also about onehalf of dimension D. Thus, if the metal of the coating bath is one like aluminum, having a tough and gummy oxide, and if the coating control element is brought closer to the level of coating metal in the bath, and if the bore ess, it is to be understood that it may be cleaned and heated to a temperature close to that of the bath by other processes which leave its surfaces suitably free from flux, pickling residues, and oxides, and sufiiciently clean to permit rapid and thorough wetting by the coating metal.

It will also be apparent that the functioning of the coating control element (21, 22) with or without the assistance of the gas finishing facility 23 is not limited only to a short immersion coating process. When applied to conventional coating pots which are commonly equipped with asbestos wipes or the like for fin shing the wire surface after coating, the coating control elements need only to be carefully centered around the strand and positioned a short distance above the surface of the bath and below the level to which a normal meniscus will bepulled by the moving strand, to produce a smooth and uniform coating. Dimensions A, B, C, and D will cooperate in the same relationships as have been described above in controlling the weight of coating on the strand.

It will be understood that various modifications may be made without departing from the spirit of the invention and it will be clear that I do not intend to limit myself except as set forth in the claims which follow.

Having now fully described my invention, what I claim as new and desire to s cure by Letters Patent is:

1. In a coating apparatus for coating a metal strand with molten coating metal, a container for molten coating metal, the bottom of said container having an orifice for the passage of said strand with clearance thereabout, means for moving a strand continuously upwardly through said orifice, means acting upon said strand before its passage through said orifice for centering the strand with respect to said orifice, and a coating control element of a material which is not wettable by said coating metal and having an aperture for the passage of said strand with clearance thereabout, said control element being disposed closely above said orifice and with its aperture aligned with the orifice in said container.

'2. In. a coating apparatus forcoatin g a metal strand with molten coating metal, acontainer for'molten coating'met'al, the bottom 5r "said container having an arise;

being above the normal level-of molten metal in'the container, means for moving-a strand continuously upwardly through said orifice, means acting upon said strand before its passage throughsaid orifice for centering the strand with respect to said orifice, and a coating control element of a material which is not wettable by said coating metal and having an aperture for the passage of said strand with clearancethereabout, said control element being disposed closely above said orifice and with its aperture aligned with the orifice in said container, said coating control element havingas a lower portion thereof, an anchoring plateof a material which is wettable by said coating metal and having an aperture for the passage of said strand with clearancethe reabout.

3. A coating apparatus according to claim 2, wherein said strand is a wire, and wherein the bottom of said container about said first namedorifice is in the form of a cone with the orifice at the apex thereof.

4. A coating apparatus according to claim 2, wherein said strand is a wire'and'wherein the means for centering said strand with respect to said first named orifice is a wire drawing die.

-5. A coating apparatus according to claim 2, wherein said strand is a wire and wherein the means for centering said strand with respect to said first named orifice is composed of two pairs at least of guide rollers acting on said strand at right angles to each other.

6. A coating apparatus according to claim 2, wherein said control element is of ceramicmaterial. v

7. A coating apparatus according to claim 2, wherein said control element is of fire clay.

S. A coating apparatus according to claim 2, wherein said control element is of porcelain.

9. A coating apparatus according to claim 2, wherein said control element is of zirconlumsilica te.

10. A coating apparatus according to claim '2, wherein said anchoring plate is oftitanium bearing cast iron,

11. A coating apparatus according to claim 2, wherein said anchoring plate 18 of molybdenum. v

12. A coating apparatus according to claim '2, including'means for providing a protective atmosphere for said strand up to its point of entry into said container.

B. A coating apparatus according to claim 2, including means providing a protective atmosphere for said strand a the point at Wi'llCh it emerges from said control element to protect it during initial cooling at least.

l4. A coating apparatus according to claim 13, including cooling means immediately beyond said last named means to insure rap.d cooling of the'coated strand.

15. A coating apparatus accordin'g t'o claim 2, wherein the container for said coating metal is of material which is free of carbon in any form.

16. A coating apparatus according to claim 2-, wherein cooling means are provided to insure rapid cooling of the coated strand.

17. The method of coating a metal strand with a molten coating metal which comprises thoroughly cleaning said strand and raising its temperature, providing -a container having an orifice in the bottom thereof for the passage of said strand, said bottom sloping upwardly on all 'sides to the edge of said orifice, maintaining a bath of-molten coating metal in said container, moving said strand through said orifice, and pulling said'rnolten coating metal upwardly over said sloping bottom by means of said strand, and controlling the thickness of said coating on said strand by causing said strand'in freshly coated condition to pass with clearance through'a plate of'wettable materialliaving an aperture, followed immediately by "a plate ofnon-wettabl'e materialfhaving an aperture,

18. The method of coating a'metal strand withla molt ep coating rnetal'which'comprises thoroughly cleaning said strand and raising its temperature, providing a container having an orifice in the bottom thereof for the passage of said strand, said bottom sloping upwardly on all sides to the edge of said orifice, maintaining a bath of molten coating metal in said container at a level below the edge of said orifice, moving said strand through said orifice, and pulling said molten coating metal upwardly over said sloping bottom by means of said strand, and controlling the thicknessof said coating on said strand by causing said strand in freshly coated condition to pass with clearance through a plate of wettable material having an aperture, followed immediately by a plate of non-wettable material having an aperture.

19. The method of coating a metal strand with a molten coating metal which comprises thoroughly cleaning said strand and raising its temperature, providing a container having an orifice in the bottom thereof for the passage of said strand, said bottom sloping upwardly on all sides to the edge of said orifice, maintaining a bath of molten coating metal in said container, moving said strand through said orifice, causing said molten coating metal initially to contact said strand as it issues from said orifice, then lowering the level of said molten coating metal in said container below the edge of said orifice so that said molten coating metal is pulled upwardly over said sloping bottom, and controlling the thickness of said coating on said strand by causing said strand in freshly coated condition to pass with clearance through a plate of wettable material having an aperture, followed immediately by a plate of non-wettable material having an aperture.

20. The method of coating a metal strand with a molten coating metal which comprises thoroughly cleaning said strand and raising its temperature, providing a container having an orifice in the bottom thereof for the passage of said strand, said bottom sloping upwardly on all sides to the edge of said orifice, maintaining a bath of molten coating metal in said container, moving said strand through said orifice, causing said molten coating metal initially to contact said strand as it issues from said orifice, then lowering the level of said molten coating metal in said container below the edge of said orifice so that said molten coating metal is pulled upwardly over said sloping bottom, and controlling the thickness of coating on said strand by passing the freshly coated strand with clearance through a plate of wettable material having an aperture and immediately thereafter passing said strand with clearance through a member of non-wettable material having an aperture.

21. The method of claim 20 which includes the step of controlling the thickness of said coating by varying the height of said plate above the orifice in said container.

22. The method of claim 20 including the step of controlling the thickness of coating by varying the extent longitudinally of the strand of said non-wettable member.

23. The method of claim 20 including the step of controlling the thickness of coating by varying the clearance between said strand and said wettable plate.

24. The method of claim 20 including the step of pro-.

26. The method of claim 20 including the step of cooling the coated strand rapidly after it emerges from the coating control element.

27. A coating control element for use in the coating of a metal strand with molten coating metal, comprising a member of a material which is not wettable by said coating metal, and having an aperture for the passage of said strand and its coating with clearance thereabout.

28. A coating control element for use in the coating of a metal strand with molten coating metal, comprising a member having an aperture for the passage of said strand with clearance thereabout, said member at the entrance side of said strand being of a material which is wettable by said coating metal, and said member over the balance of its axial extent being of a material which is not wetted by said coating metal.

29. The method of controlling the thickness of coating on a metal strand coated with a molten coating metal, which includes the step of passing a freshly coated strand, with clearance for said strand and its coating, through an apertured plate of a material which is not wettable by said coating metal.

30. The method of controlling the thickness of coating on a metal strand coated with a molten coating metal, which includes the steps of passing a freshly coated strand, with clearance, through an apertured plate of a material which is wettable by said coating metal, and immediately thereafter passing said strand, with clearance, through an apertured member of a material which is not wetted by said coating metal.

31. The method of coating a metal strand with a molten coating metal having a tough and gummy oxide which comprises thoroughly cleaning said strand and raising its temperature, providing a container having an orifice in the bottom thereof for the passage of said strand, maintaining a bath of said molten coating metal in said container, moving said strand through said orifice, and pulling said molten coating metal upwardly by means of said strand, and controlling the thickness of said coating on said strand by causing said strand in a freshly coated condition to pass with clearance through a plate of nonwettable material having an aperture.

References Cited in the file of this patent UNITED STATES PATENTS 590,965 Cook Oct. 5, 1897 1,033,912 Lendi July 30, 1912 1,096,688 Dantsizen May 12, 1914 1,551,751 Kozak Sept. 1, 1925 1,994,802 Adams Mar. 19, 1935 2,070,035 Weiss Feb. 9, 1937 2,110,893 Sendzimir Mar. 15, 1938 2,136,957 Sendzimir Nov. 15, 1938 2,197,622 Sendzimir Apr. 16, 1940 2,315,725 Moller Apr. 6, 1943 2,394,545 Grupe Feb. 12, 1946 2,536,186 Keller Jan. 2, 1951 FOREIGN PATENTS 496,402 Great Britain Nov. 30, 1938 631,817 Great Britain Nov. 10, 1949 

1. IN A COATING APPARATUS FOR COATING A METAL STRANDWITH MOLTEN COATING METAL, A CONTAINER FOR MOLTEN COATING METAL, THE BOTTOM OF SAID CONTAINER HAVING AN ORIFICE FOR THE PASSAGE OF SAID STRAND WITH CLEARANCE THEREABOUT, MEANS FOR MOVING A STRAND CONTINOUSLY UPWARDLY THROUGH SAID ORIFICE, MEANS ACTING UPON SAID STRAND BEFORE ITS PASSAGE THROUGH SAID ORIFICE FOR CENTERING THE STRAND WITH 